Dol starter or just a plug is it really worth it?

[not done it yetParticipant @notdoneityet]

As a lathe should never be left running unsupervised, you should be able to tell if the motor is overloaded and avoid it, or investigate why. A stalled situation is no different, really – you hit the stop button or emergency stop immediately.

So, while overloads are good to have, they are not as important as the no volts protection against unexpected restart.

[Grant Allen 1Participant @grantallen1]

Brilliant thanks Nick. I'll place an order for a dol switch with overload of 2-5 amp that should cover everything. I already have an e.stop so I'll have to work out hove to wire that in when its here. I assume a plug on the other end is a suitable way of turning power of to the machine surely it wouldn't require a main isolation switch?

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Grant, yes if your DOL system is within the power rating of a normal household socket of 13 amps, a plug is OK, anything higher and you would have to use an industrial plug and socket with an appropriate MCB/fuse or wire it into an isolation outlet.

Regards Nick.

[Grant Allen 1Participant @grantallen1]

Cheers for your help. Looking at being able to reverse the motor I assume would be not easy?? I've checked the induction motor and you can wire it to rotate both ways but only by changing connecting rods to different pins.

[SillyOldDufferModerator @sillyoldduffer]

I wouldn't fit a DOL to a small single-phase motor on a 1947 Myford.

• As most DOLs are 3-phase, Grant might have fun adapting the overload wiring for a single phase motor.
• How much current should the overload take? It depends on the motor and all I know is single-phase motors draw more start-up than a 3-phase. Too low, and the DOL will stop the motor, too high and it won't protect the motor.

'Kedu Switch' had me going until I found KEDU is a Trade Name for a wide range of electrical products including No Volt Release switches like this KJD17 NVR Switch on ebay. I would say this is exactly what Grant needs. NVR with a suitable fuse in the plug is good enough for a hobby lathe. The overload protection provided by a DOL is more appropriate to a machine that's worked hard over long periods, and that's not likely to happen to Grant's Myford. (Unless he knows different!)

One reason a DOL might be preferred is they look more in keeping with classic machines. Bright Yellow plastic switches with easy to hit Red and Green buttons aren't exactly sympathetic to a lathe made in the year soft toilet paper was first sold in the UK.

Dave

Historic Footnote: Before 1947 Englishmen used Emery Paper to keep themselves fresh because it never wore out. You just can't get quality bog-roll today…

[Grant Allen 1Participant @grantallen1]

I have not ordered anything yet, as I keep coming back to the kedu brand switches, I used for so many things in the past and have never had any trouble. Looking at the dol switches I do agree its abit over the top but is that better to be or not. The only thing I'm unsure of is can you add a e.stop to one like mentioned in the post previous?

[Ian PParticipant @ianp]

SOD has summed up much better what I tried to say in my earlier reply. The additional information on toilet paper enhances the thread too.

Ian P (no longer a user of Izal)

[Simon Williams 3Participant @simonwilliams3]

Er…

One of those yellow pushbutton kedu type switches is by definition a direct on line (DOL) connector (switch) though the convention is that the word "starter" indicates that an appropriately sized overload device is included. As several have said, yer gets yer no volt release (NVR) function either way.

The IET wiring regs (BS7671) determine that a overload protection device must be fitted to automatically disconnect the supply to a motor in the event of overload (usually overcurrent) if the motor is over a certain size. From memory that size is 0.375 Kw (1/2 HP). A motor thermal overload relay is a far more sensitive device than any of the usual types of MCB in that it is designed to imitate the thermal characteristic of a motor and monitor its recent service history as well as the presence of an instantaneous fault. An MCB – even of the various different types (A, B, C or D) – is a different beast entirely..

Small overloads do exist, but below 0.375 Kw it's a bit of a lottery, as the current/load characteristic of small induction motors is a black art, and needs to take into account the phase angle of the load current. So protecting a small (sub 1/2 HP) motor with a plug top fuse isn't ideal, but is probably as good as it gets without major complication.

Using DOL starters on single phase is easy enough, provided the coil voltage for the maintain/NVR function is 230 volts not 400 as it might well be on a starter designed for three phase use. Remember to double back the load current through the spare poles of the overload on a three phase starter used on single phase so all three poles of the overload see the same current, as most are sensitive to current imbalance and will trip if one pole is left unused.

HTH Simon

 

 

Edited By Simon Williams 3 on 26/04/2019 14:15:37

[Grant Allen 1Participant @grantallen1]

So, do I get a nvr switch or a single phase 240v dol starter with overload 2.3- 4 amps both are the same price both will have a 5amp plug on. So running a .37kw motor maybe wishing to add to an e stop and motor reverse switch would determine which one

Kedu nvr switch

Or

240v dol starter overload 2.3-4amps

[Simon Williams 3Participant @simonwilliams3]

Posted by Grant Allen 1 on 26/04/2019 14:32:07:

So, do I get a nvr switch or a single phase 240v dol starter with overload 2.3- 4 amps both are the same price both will have a 5amp plug on. So running a .37kw motor maybe wishing to add to an e stop and motor reverse switch would determine which one

Kedu nvr switch

Or

240v dol starter overload 2.3-4amps

For the same price go with the extra protection and adaptability of the single phase push button starter with an overload device and the option of a remote E Stop. I take the point from an earlier contributor that it's a bit anachronistic, but not as much so as the yellow pushbutton thing. Either way, that's the price you pay for bringing modern day safety technology into a 60 year old environment.

Besides, if as you say the Kedu type switch would have a cable to a 5A plug, (which won't be locally fused?) where is your overcurrent protective device and what rating would it be? And what else would it have on the same circuit?

Rgds Simon

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Grant, if you want to go with the Kedu type NVR and have extra E-stops, then you need this type **LINK** this has a fifth terminal to wire in extra cut-outs or stops. You may like to refer to this post **LINK** for a bit more info.

Regards Nick.

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